Yes, metadata can be altered, hence the the original question, how that photo was dated?
The same way photos have always been dated - by the use of various bits of supporting evidence, none of which are immune to manipulation.
If you want to know when it was taken with 100% certainty, then that is impossible - but only in the sense that nothing you didn't see yourself can be certain; a favourite PRATT of the creationists. How do you know? Were you there?
You can't even prove that Russia exists; I believe that I flew over Russia a few times on flights from Australia to Europe and vice-versa; but I only have the airline's word for it - for all I know they could have been flying round in circles over Poland, or China, or Alice Springs, while the map showed the little plane icon inching its way across the Caspian Sea, and then over Russia and Ukraine.
For all I know, the whole nation is an elaborate hoax, and the area between the East coast of Belarus and the West coast of Alaska is all ocean.
Indeed, the entire world could be about 2000km across; with a high resolution video playing in the "windows" of intercontinental airliners, while the plane sits on a shaking platform, and thousands of scenery shifters get rid of all the British foliage, animals, towns and climate, and replace them with Australian ones, while I try to sleep on the long "flight".
It is easy to make everything seem doubtful - whether it is actually the truth or a lie. But it is harder to make a lie seem real - hence the sudden disappearance of the 'most likely' idea that MH017 was shot down by a Ukrainian fighter jet with an air to air missile (remember that 'hypothesis'?)
Now perhaps the plane wasn't shot down by Russian-backed separatist rebels. But if it wasn't, we need a better hypothesis to replace that one - an hypothesis that fits ALL of the facts as well as, or better than, the separatist rebels hypothesis. It's not enough to cast doubt on the leading hypothesis, because you can cast doubt on ANYTHING. What you need to do is to find a plausible alternative. And that has proven impossible.
The 'Ukrainian air to air hypothesis' was garbage, and has quietly been dropped by its proponents.
The 'Ukranians with their own BUK' hypothesis is less awful, but it has one GLARING problem - whoever shot down the plane was trying to shoot
something down. And the only plausible airborne targets in the area at the time were Ukrainian.
It is believable that Russian or Russian-backed forces who somehow had a BUK might see an aircraft approaching from the West on their radar, and decide it was probably a Ukrainian aircraft, and worth taking a shot at - the separatists were already enjoying taking down Ukrainian military aircraft in the area, and were quite proud of their successes in doing so. Few if any Russian aircraft were in that airspace; certainly they were not flying combat support missions or otherwise doing things that might inspire the Ukrainian forces to try to shoot one down; and as the airspace was controlled by, and used by, the Ukrainian military, any Ukrainian anti-aircraft unit would have been very aware that most (if not all) targets in the skies above them were friendlies - making identification a priority before opening fire.
The Separatists, on the other hand, could quite reasonably have had an 'if it flies, shoot it' policy, 'knowing' that all air traffic above them was enemy traffic. All that would require was an unawareness that international civil air traffic used a corridor above their war zone.
The question that must be answered is simple - we can assume that whoever shot down MH017 believed that they were engaging a legitimate enemy target. If the Russians, or the separatists, thought it was another Ukrainian military aircraft, then that explains that. But if the Ukrainians were the ones who shot it down, the question is "What did they THINK they were shooting at?".
This wasn't the 4th of July, when they just fired a rocket for shits and giggles. It was an aimed shot at a (presumably misidentified) target. So what was the target believed to be? A plane coming from the direction of Kiev, in airspace dominated by Ukrainian aircraft, is a very strange target for a Ukrainian anti-aircraft unit to engage without 100% positive ID.